This study investigates parents' lived experiences of having a child diagnosed with Attention Deficit Hyperactivity Disorder (ADHD). The aim was to explore parents' meaning-making processes in relation to their children's ADHD with a focus on understanding the impact that receiving a diagnosis had on the parents' perceptions of, and ways of managing, their children's challenging behaviours. Drawing on data collected through semi-structured interviews with 12 parents, we carried out a content analysis of the parents' accounts, producing a range of categories describing different aspects of the parents' meaning-making processes in relation to their child receiving an ADHD diagnosis. Five conceptual categories were identified, describing components of a process of adaptation through which the parents -- using the diagnosis as a tool -- were able to transform feelings of distress over their difficulties in managing their child's challenging behaviours into feelings of being able to cope with these challenges of integrating the ADHD diagnosis into everyday family life. This research suggests that understanding the long-term processes involved in parents' meaning-making of an ADHD diagnosis is important and can open up a pathway to developing initiatives to support parents in dealing with their child's challenging behaviours in everyday life.